DISCUSSION OF RESULTS OF CRUISE IV OF THE CARNEGIE. 



The present compilation and discussion concerns itself prmiarily with the Carnegie's 

 fourth cruise, but in so far as it includes a comparison of the data with those of former 

 observers, it also serves as a general review of the present status of ocean atmospheric- 

 electric observations. 



The results for the daily detenninations of the various elements are recorded in Tables 

 79-83, each table corresponding to one leg of the cruise. Apart from the observations on 

 the diurnal variations, the measurements were always taken about the same time of day. 

 The times recorded in the tables, which are local mean tunes, refer to the mean times during 

 the determinations of the potential-gradient, conductivity, and ionic content, and the 

 mean of these times for the whole cruise through March 1916 is 9*'7. The observations 

 for the three elements referred to extended over a period of about three-quarters of an hour, 

 the collection of the active material occurring during the last half hour of the period, or 

 occasionally after the completion of the period. The measurement of the penetrating 

 radiation followed inunediately after the determination of the other elements, and it will be 

 sufficient to look upon the determinations of this element as corresponding to a mean time 

 one hour later than the times recorded m the tables. The observations for the diurnal 

 variations are not shown in the tables, but will be discussed separately. 



The mean values of the quantities for each passage of the cruise are recorded in Table 84. 

 The number of daily sets of observations involved in the determination of each mean is 

 shown by the figures in parentheses, and in taking the means, each observation has been given 

 equal weight. This was felt to be the fairest plan on the whole, since any attempt to weight 

 the observations according to such conditions as the extent of the roll of the ship, for 

 example, would implicitly involve attaching small weight to those observations corresponding 

 to high strengths of wind. One set of computations was carried out for the first three rows 

 in Table 84, weighting the observations according to the magnitude of the leak correction, as 

 the determination of this correction seemed to be one of the main sources of error in the 

 earlier sets of observations, although the correction was usually zero in the later observa- 

 tions. Only in the case of the voyage from Brooklyn to Colon, for which there were very 

 few values, and where the means were largely controlled by one or two abnormal values, 

 was any appreciable difference produced in the mean by this method of treatment. 



Although, in view of the wide range of variation in the Atlantic-Ocean values of the 

 conductivity and ionic content (see Table 79), no great weight is attached to these values 

 as representative of normal conditions, it must be pointed out that the close agreement 



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